Mining apparatus and advancing means therefor



Oct. 15, 1963 K. BARALL ETAL 3,106,825

MINING APPARATUS AND ADvANcING MEANS THEREFOR Filed June '7, 1960 3 Sheets-Sheet 1 Mdr nrramlsv Oct. 15,-1963 K. BARALL ETAL 3,106,825

MINING APPARATUS AND AnvANcING MEANS THEREFOR Filed June 7, 1960 s sheets-sheet 2 NWN/M@ M /MM C i` a f .Im/enfans Oct. 15, 1963 K. BARALL ErAL 3,106,825

MINING APPARATUS AND ADvANcING MEANS THEREFOR 3 Sheets-Sheet 3 Filed June 7, 1960 Mair @Trae/VFY United States Patent O M 3,106,825 il" G APPARATUS AND ADVANCNG MEANS THEREFQR Karl Barall, Duisburg-Buchholz, Wilhelm Willienloh,

Duisburg-Wanheirn, and Friedhelm Kiihnapfel, Duisburg-Buchholz, Germany, assignors to Rheinstahl Wanheim Grmbl-I., Duisburg-Weinheim, Germany Filed .lune 7, 1964i, Ser. No. 34,531 Claims priority, application Germany .lune 9, 1959 l Claims. (Cl. 61-45) The present invention relates to mining apparatus in general, `and more particularly to la mining apparatus which is combined fwith novel advancing means adapted to move its units in step-by-step fashion toward the mine face in an underground excavation. Still more particularly, the invention relates to a mining yapparatus which comprises twvo elongated prop units and a rack-and-pinion arrangement which is combined with the prop units in such a way that the prop units may be vadvanced toward the mine face and that the component parts of the rack and pinion arrangement may be utilized for moving a conveyor toward the mine face.

It is already known to utilize mining apparatus which comprise two or more prop units combined with advancing means adapted to move the prop units with respect to each other in order to follow the mine face during a mining operation. The advancing means comprises hydraulic or pneumatic piston-cylinder assemblies whose components are respectively coupled with the individual prop units to shift the prop units with respect to each other upon introduction of a hydraulic or pneumatic pressure fluid. The disadvantage of such conventional advancing means is that the steps performed by the prop units during their advance toward the mine face are rather short and usually do not exceed one-half the length of a prop unit.

An important object of the present invention is to provide a mining apparatus which embodies novel advancing t `cans and which may be advanced in step-by-step fashion in such a way that the length of individual steps at least equals but may greatly exceed the length of the prop units.

Another important object of the invention is to provide a mining `apparatus of the above outlined charactenistics which is of fvery compact design and which may be utilized as a means for 'advancing the customary conveyor toward the mine yface.

-A further object of the invention is to provide a mining apparatus of the above described character which is constructed and assembled in such a way that it is capable of advancing the interconnected prop units over extremely rough terrain and in which .the advancing force may be varied to insure that the conveyor or the prop units may be advanced regardless of the conditions prevailing in the mine.

A concomitant object of the invention is to provide a mining apparatus of the type comprising two aligned prop units and a mechanical arrangement for advancing the prop units in step-by-step fashion with respect to each other, in which the component parts of the advancing mechanism may be readily replaced or exchanged if it should become necessary to increase or shorten the length of steps by which the units are advanced with respect to each other.

Still another object of the instant invention is to provide a mining apparatus of the above outlined characteristics in which at least certain components of the advancing mechanism may be readily separated lfrom the prop units for use in advancing the prop units forming pant of other mining apparatus. l

An additional object of the invention is to provide a mining apparatus of the above described character in A, ananas Patented Oct. 15, 1963 which the interconnected component parts of each prop unit are movable in all directions with respect to each other so that the prop units may be readily installed in excavations bounded by very uneven and rough walls Without reducing the safety of the mining apparatus, and in which the component parts o each prop unit always tend to return to their normal positions.

With the above objects in view, the invention resides in the provision of a mining 4apparatus which comprises essentially two aligned prop units, two toothed rac-ks each of which may be connected with one of the prop units, coupling means for slidably connecting the racks in such manner that the racks are shiftable relative to and in parallelism with each other, and means for shifting the Iracks relative to each other, the shifting means comprising floating pinion means in permanent mesh with the teeth of both racks and rotating means in the form of a motor which is adapted to rotate the pinion means and which is preferably separably secured to the gear case in which the pinion means is mounted.

Tihe novel features which are considered as characteristic for the invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together 'with additional objects and advantages thereof, will be best understood from the following detailed description of certain specific embodiments when read in connection with the `accompanying dnawings, in which:

FIG. l is a top plan view of a mining apparatus embodying one form of our invention lwith the caps on both prop units removed land with a portion of the coupling device broken away;

FIG. 2 is a side elevational view of the mining apparatus;

FIG. 3 is an enlanged fragmentary transverse section taken along the line III-III of FIG. 2, as seen in the direction or" arrows;

FIG. 4 shows the appanatus of FIGSQl to 3 in an eX- eavation in a position ready to advance a conveyor toward the mine face;

FIG. l5 is a top plan View of the appanatus shown in FIG. 4 with the two prop units in staggered relation;

FIG. 6 illustrates the step of advancing the conveyor toward the mine face;

FIG. 7 illustrates the apparatus of FIGS. 4 to 6 in a different position Iafter the two prop units are advanced toward the conveyor;

FIG. 8 is a top plan view of a slightly modified mining apparatus;

FIG. 9 illustrates the mining -appanatus of FIG. 8 in a different position; and y FIG. 10 is an enlarged fragmentary yfront elevational view of the modified mining apparatus as seen in the direction o-f arrows from the line X-X of FIG. 8.

Referring now in greater detail to the illustrated embodiments, and iirst to FIGS. l to 3, the mining apparatus therein shown comprises essentially two elongated prop units A and B 'of identical design and arranged in mirror reverse with respect to a symmetry plane passing horizontally through the center of 2. The prop units are coupled with and are movable in step-by-step fashion relative to each other so that they may advance a conveyor toward .the mine face and also to prop up a portion of the mine roof during the mining operation.

The coupling device assumes the form of a slide rail 24 which will be described in greater detail hereinafter.

The prop unit A comprises two aligned hydraulic props l, 2 in the form of extensible and contractible jack assemblies each of which includes a tubular lower component la, l2a and a tubular upper componen-t lb, 2b which is telescopically received in the respective lower Y 3 component. The lower components 1a, 2a are articulately mounted on two aligned skid plates 3, 4, respectively, and the upper ends of the upper components 1b, 2b articulately support two interconnected sections 16a, b of a composite cap 10.

The prop unit B comprises two props or jacks 15, 16, two skid plates 17, 1:8, and a composite cap 1G which is shown in FIGS. 4 to 7. The articulate connection between the lower component a of the prop 15 and its skid plate 17 is shown in greater detail in FIG. 3. The lower end portion of the component 15a is received in an upwardly opening cupped holder 5b whose underside carries a hemispherical head 5 extending into the complementary concave recess of a socket `5a which is secured to the upper side of the skid plate 17. The cupped holder 5b is rigidly connected with an annular cover member 6 which rests upon a loose ring 6a and is received in the opening of an inwardly extending annular ilange forming part of a vertical sleeve 6b, the latter being secured to and extending upwardly from the skid plate 17 so as to concentrically surround the socket 5a. The outer diameter of the ring 6a is greater than the diameter of the opening in the flange of the sleeve 6b so that the ring cannot be withdrawn through said opening.

The means for permanently biasing the prop 15 into vertical position comprises three or more elastic cushions or pads 7 (only one shown in FIG. 3) which are preferably uniformly spaced along and extend downwardly from the peripheral portion of the cover member 6. The elastic cushion 7 shown in FIG. 3 is held between the underside of the oating ring 6a and between the upper side of a compressing washer 7b, the latter being formed with a threaded bore and being held in the illustrated position by a threaded bolt 7a whose head engages the upper side of the cover member 6 and which extends freely through aligned holes provided in the cover member 6, in the ring 6a and in the cushion 7. The just described mounting of the lower prop component 15a insures that the prop `l5 is constantly biased into vertical position regardless of the direction in which it is inclined from a vertical position. This is due to the fact that one or more cushions 7 are compressed whenever the lower component 15a is tilted, i.e. whenever the hemispherical head 5 changes its position in the socket 5a. Thus, and assuming that the lower component 15a is tilted in a direction to the left of FIG. 3, the cover member 6 will be tilted with it and its left-hand portion will enter through the opening of and into the interior of the sleeve 6b thereby entraining the ring 6a so that the latter compresses the cushion 7 because the bolt "7a abuts against the skid plate 17 and because it is not positively connected with the parts 6, 6a, 6b and 7 but only with the washer 7b. Consequently, the cushion 7 will immediately return the lower prop component 15a to its vertical position as soon as the tilting force is terminated. On the other hand, if the prop component 15a is tilted in direction to the right, the upper side of the cover member 6 will act against the head of the bolt 7a and will move the bolt, as well as the washer 7b, in a direction away from the skid plate i17. Since the ring 6a is entrapped in the sleeve 6b, the cushion 7 is compressed between the underside of this ring and the upper side of the -washer 7b so that the cushion stores energy and returns the prop component 15a to its vertical position when the tilting force is terminated. =ln other words, any tilting movements of the prop 1.5 invariably cause a compression of each cushion 7. The mounting of the props 1, 2 and 16 on their respective skid plates 3, 4 and 18 is analogous.

Inv the position of FIGS. 1 and 2, the mining apparatus is intended to advance in a direction to the left. Therefore, the front ends of the skid plates 3, 4, 17 and 13 are formed with upwardly inclined extensions Sil which prevent jamming when the skid plates must advance along a rough mine floor. The skid plates 3, 4 of the prop unit A are connected by two parallel bands 8, 9 of spring steel or the like so that they may be inclined with respect to each other if the configuration of the mine floor renders such inclination necessary. The skid plates .17, 18 of the prop unit B are connected by similar spring steel bands 19 and Z0.

The composite cap l1t) of the prop yunit A comprises the aforementioned sections 10a, 1Gb which are articulately connected by a pivot pin 13. The rear cap section 10b is formed with a bifurcated front end portion comprising the arms 10b', 10b" (see FIG. 5) each of which is formed with an elongated closed slot 11, these slots being transversely aligned so that they may receive a locking wedge 12. The arms 1Gb', 13b are further formed with two transversely aligned openings which rotatably receive the aforementioned pivot pin l13, this pin also passing through an opening provided in the suitably contigurated rear end portion 19a' ot the front cap section 16a, the end portion 10a extending into the space defined by the arms Mib', 10b" of the rear cap section 1Gb. In addition, the end portion 10a is formed with a suitably inclined face 10a" (see FIG. 2) which cooperates with the wedge 12 so as to prevent angular movements of sections lila, 10b when the wedge is inserted into the aligned slots 11. FIG. 2 also illustrates that the upper end of the prop component 1b is formed with a hemispherical head 14 which is received in a socket 14a provided in the front cap section 10a so that this cap section may be articulated with respect to the prop 1. The mounting of the other cap section 10b ou the prop 2, as well as the mounting of sections constituting the cap 10 of the prop unit B on their respective props 15, 16 is analogous. `In addition, the sections of caps I10, lil' are mounted on cushions similar to the cushion 7 shown in FIG. 3 so that each cap is automatically returned into a horizontal position as soon as the tilting forces which might act thereagainst are terminated, i.e. whenever the caps are separated from the roof of an excavation. lt will thus be noted that the main elements of each prop unit are connected with each other in such manner that they may perform movements in any desired direction but that they are permanently biased into a neutral or unstressed position as soon as the deforming stresses are terminated. The skid plates of each prop unit are movable to a given extent with respect to each other owing to the provision of spring steel bands 8, 9 and 19, 20; the lower ends of the props are tiltable owing to the provision of elastic cushions 7; the cap sections are articulatable about the pivot pins A13; and each cap section is pivotable on the upper end of the respective prop component owing to the provision of universal joints 14, 14a and of the non-illustrated elastic cushions which operate in the same manner as the cushions 7 of FIG. 3.

The means which permits vertical and longitudinal displacements of the prop unit A with respect to the prop unit B and vice versa will now be described with reference to FIGS. l to 3. The prop unit A comprises two comparatively short upright guide members 21 of kl-bar stock which are mounted on the skid plates 3, 4 forwardly and rearwardly of the steel band 9, respectively. Two similar I-shaped guide members 21 are mounted on the skid plates 17, 18 of the prop unit B forwardly and rearwardly of the steel band 19, respectively. Each of these guide members 21 mounts a spacer element 22 in such manner that each spacer element is vertically slidable along the adjacent flanges of the respective guide bar. To that end, the spacer elements 22 are provided with suitably conigurated pairs of aligned vertical claws 22a which extend toward the webs 21a of the respective guide members. Adjacent to its upper end, the web 21a of each guide member carries a transverse stop 23 (see FIG. 3) which prevents complete removal of the respective spacer element 22. Each spacer element 22 is further provided with a pair of aligned horizontal claws 22b which are slidably guided along the adjacent anges of a coupling device in the form of a horizontal slide rail 24 which preferably assumes the shape of an H-bar (see FIG. 3). This coupling device or slide rail is located between the prop units A, B but has no positive rigid connection with either of these units, i.e. the sole connection betwen the -units A, B and the rail 24 consists of the claws 225 forming part of the spacer elements 22 which latter, in turn, are vertically slidable along the guide members 21. Owing to such connection, the rail 24 may be shifted vertically together with the spacer elements 22 when the skid plates 3, 4 are located above the level of the skid plates `17, 18, or vice versa. Furthermore, one of the prop units may move along the rail 24 while the other prop unit remains stationary, or one of the prop units may be simultaneously displaced vertically as well as longitudinally with respect to the other prop unit. The length of the slide rail 24 preferably at least equals but may exceed twice the distance between the props 1, 2 or 1S, 16 (see FIGS. 4 to 7). In order to prevent complete separation of the spacer elements 22 from the rail 24, the forward and rear ends of the flanges forming part of the rail 24 carry pairwise arranged stop pins 25, 26, respectively.

The above described loose connection between the prop units A, B by means of guide members 21, spacer elements 22 and slide rail 24 enables the prop units to advance in step-by-step fashion with respect to each other. During such movement, one of the prop units moves along and/or with the slide rail 24 while the other prop unit remains stationary, or vice versa. The manner in which such movements are carried out and the purpose of such movements will be described in connection with FIGS. 4 to 7. 'Ihe length of the movements which one of the prop units may perform with respect to the other prop unit equals or exceeds twice the distance between the aligned props 1, 2 or 1S, 16, depending upon the length of the slide rail 2,4. The stop pins 25 at the forward end of `the slide rail 24 serve as a means for entraining the rail in forward direction when the prop unit A advances with respect to the temporarily arrested prop unit B, or vice versa.

The means for advancing the prop units in stepwise fashion comprises two toothed racks .27, 28 which are preferably readily separably connected with the prop units A, B, respectively. These racks are mounted above the respective pairs of spacer elements 22 and are disposed in such manner that their teeth 27a, 28a extend in two parallel rows and that the teeth 27a of the rack 27 face the teeth 28a of the rack 28. At each of their ends, the racks 27, 28 are releasably connected with guide clamps 29 which are forwardly adjacent to the respective spacer elementsvZZ, i.e. each guide clamp 29' is closer to the forward stop pins 2S than the adjacent spacer element 22. The clamps 29 engage the flanges of the rail 24 so that the racks 27, 28 are slidable along this rail but normally cannot be separated therefrom because the clamps 29 will come into abutment with the stop pins 25 as soon as the forward end of a rack reaches the forward end of the slide rail 24. Thus, the clamps 29 constitute means for longitudinally slidably or shiftably connecting the racks 27, 28 with the coupling device or rail 24. The length of each rack preferably equals or approximates the length of the prop units A, B. The preferably separable connection betwen the racks 27, 28 and the respective prop units A, B comprises forked connectors 36V which extend into aligned notches formed in the racks and in the spacer elements 22 therebelow (see FIG. 3). These readily separable connectors 30 prevent longitudinal displacement of the racks 27, 28 with respect to their prop units but permit vertical displacement of the racks when the spacer elements 22 move along the guide members 2d. As stated before, the mounting of spacer elements 22 on the vertical guide members Z1 insures proper support for the skid plates when the prop units must advance along a rough or uneven mine iloor. 4If the rack 27 is caused to advance beyond the position of FIG. 2, its front guide clamp 29 comes into abutment lwith the stop pins 25 and entrains the slide rail 24 in the same direction. Similarly, the front guide clamp 29 of the rack 2S will engage with the stop pins 25 when the prop unit B is shifted forwardly (to the left) from its position of FIG. l. Of course, the racks 27, 28 may be provided with means other than the clamps 29 for engaging with the stop pins 25 at the forward end of the slide rail 24 and for entraining this rail with the respective rack when the latter is shifted.

The :teeth 27a, 28a of the racks 27, 28 mesh with a driving pinion 31a which is mounted in the gear case 31 of a reducing gear assembly, the latter including a non- Vcircular drive shaft 32 which is connectable to and may be rotated by a suitable motor P. This motor may be a portable pneumatic motor, an electric motor or any other suitable motor which can be safely Iutilized in a mining excavation. rPhe gear case 3'1 is in sliding engagement with the racks 27, 28 and travels with one of the racks when the otherrack is advanced by the pinion 31a, or vice versa.

The improvedr mining apparatus is operated as follows:

As shown in FIG. 4, the mining apparatus is intro'- duced into an excavation which is bounded by the mine face 3-7, by the mine floor 36, by the mine roof 35, and by the mine filling 38. Immediately in front of the mine face 37, there is provided a conveyor 39 which may be of any suitable type, eg. a double chain conveyor. FIG. 5 illustrates the mining apparatus in top plan view and in a position in which the prop unit A s shifted forwardly with respect to the prop unit B by a distance equal to fthe spacing between the props `1, 2, or 15, 16. The direction of advance is indicated by the arrow C. The front spacer element 22 of the unit A is adjacent to the for-ward end of the slide rail 24, and the rear spacer element of the unit B is adjacent to the rear end of the rail. Thus, the racks 27, 28 are shifted with respect to eaoh other by a distance somewhat less than the length of a singlerack. v

FIG. 6 shows the conveyor 39' in a new position closer to the mine face which latter is not shown because it is assumed that a certain depth of the vein was removed to such an extent as to necessitate anadvance of the conveyor into the new position. The conveyor is advancedV by an extension in the form of a push rod 441 which is removably secured to the forward end of the rack 28 andex-tends in the ydirection indicated by the arrow C, i.e. the push rod constitutes an aligned extension of the rack 28. When the rack 28 is utilized for advancing motor P, not shown in FIGS. 4 7, is started to rotate the pinion 31a vanticlockwise, as viewed in FIG. 6, and to advance the rack 2S in forward direction whereby the push rod 40 shifts the conveyor 39 into and, if necessary, beyond the position of FIG. 6. Of cou-rse, the hydraulic jacks .or props 1, 2, 15, 16 are then in operative positions and rmly press the caps 10, 10" against the mine roof 35 while the skid plates 3, '4,' 17, 13 are simultaneously pressed against the mine door 36, i.e. the prop units A, B are firmly held against movements with respect to the surrounding walls yof the excavation and can take up the forces arising when the conveyor 39' is pushed in the direction of the arrow C. The motor P and the gear case 31 participate in movements of the rack 28 and the lower par-t of Ithe gear case 351 preferably assumes the and reaches the forward end of the rack 27 when the rear end of the rack 23 is close tto the pinion 31a. This position is not shown in the drawings; FIG. 6 merely shows the gear case 3-1 midway between the racks 27, 28 so that both ends of the racks are transversely aligned with each other. The detached rack 28 advances toward the mine face at twice the speed at which the gear case 31 advances along the stationary rack 27. Consequently, the distance covered by the gear case 31 also equals only half the distance covered by the rack 28. This can be observed by comparing FIGS. 5, 6 and 7 showing that the gear case 31 advances from the rear end to the forward end of the xed rack 27 while the rack 28 at the same time covers a distance twice its own length.

When the push rod 40 shifts the conveyor 39 into or beyond the position of FIG. 6, the rack 28 is withdrawn into the position of FIG. and the push rod is then separated from the latters forward end. In the next step, the operator restores the connectors 30 so that the rack 28 is again positively connected with the prop unit B. During all such movements of the rack 28, the caps 10, 1G and the skid plates 3, 4, 17, 18 lirmly hold the prop units against movement with respect to the walls of the excavation.

The forward movement of the conveyor 39 may be brought about in a dierent way by mounting the push rod 4i) directly on the gear case 31. Of course, the conveyor is then advanced at yhalf the speed of the speed attainable if the push rod is connected with a detached rack in the manner as described above. However, the pushing force is doubled. During such advance of the conveyor by the push rod 4% which is connected to the gear case 31, Ithe rack 28 remains disconnected from the prop unit B but does not participate in pushing of the conveyor because it merely slides along the rail 24 and remains in mesh with the pinion 31a.

When the conveyor 39 reaches the position of FIG. 6, the prop unit B may be shifted `into the position of FIG. 7. Before the unit B is actually shifted, its props 1-5, 16 are shortened, i.e. the upper components of these props are caused to penetrate somewhat deeper into the respective lower components so that the cap is separated from the mine roof 35 and that the skid plates 17, 18 are freely slidable along the mine floor 36. However, the props 1, 2 of the unit A remain in operative position and prevent the unit A from participating in movements of the unit B. Thus, the unit A serves as a means for taking up the reaction forces developing when the skid plates 17, 18 slide along the mine oor. Once the cap 1D and the skid plates 17, 18 are disengaged, the motor P is operated to rotate the shaft 32 and the pinion 31a which is rotated anticlockwise causes the rack 28 to travel in the direction indicated by .the arrow C while the rack 27 remains stationary. Of course, the connectors 3u are inserted when the rack 28 moves so as to insure that the entire prop unit B will participate in such movement. As mentioned before, the distance covered by the prop unit B between the positions of FIGS. 6` and 7 approximates twice the distance between the props 1, 2 or 15, 16. During such advance of the prop unit B, the rack 28 travels along the coupling device or rail 24 which latter is stationary but, as soon as the front guide clamp 29 of the rail 28 reaches the stop pins 25, the rail 24 participates in the movements of the unit B until its rear stop pins 26 come into abutment with the rear guide clamp 29 on the stationary rack 27. The front guide clamp of the rail 28 comes into abutment with the pins 25 at a time when the rack 28 is aligned with the rack 27, i.e. in the position of FIGS. l and 2. The operation is then repeated by attaching the push rod 40 to the forward end of the rack 27 and by disconnecting this rack from the prop unit A so that it may travel along the rail 24 in the direction of the arrow C in response to clockwise rotation of the pinion 31a and that it thereby shifts the conveyor 39 a requisite distance toward the new mine face. Alternately, the push rod 40 may again be connected to the gear case 31 so that the conveyor is advanced at a lower rate of speed but is moved with a `doubled force. The push rod 40 will be connected directly with the gear case 31 whenever the force exerted by the advancing rack 27 or 28 is not sutiicient to shift the conveyor to its new position.

The doubled force generated by the gear case 31 may also be utilized for advancing the prop units A and B if the force of the racks 27, 28 is not suiiicient to bring about such movements. To that end, the gear case 31 is directly connected with that prop unit which `requires shifting, for example, by a chain 48a (see FIG. 7) or by another separable connecting means. Of course, if the chain 48a is utilized for advancing say the prop unit A, the rack 27 is disconnected from this unit by removing the corresponding connectors 30 so that the unit A then advances at a lesser speed but is drawn toward the mine face with a doubled torce.

it will be readily understood that each prop unit may comprise three or more hydraulic or pneumatic props and that the number of skid plates may be increased accordingly. Also, the pinion 31a may be driven manually, eg. by connecting the non-circular shaft 32 with a hand crank or the like. Since the racks 27, 28 may be readily :disconnected from the respective prop units, these racks may be utilized for advancing one or more additional mining apparatus particularly since the motor P, too, is readily separable from the shaft 32 and because the gear case 31 need not even be removed from the racks when the racks are separated from the prop units A, B.

The length of each rack may be increased by coupling the same with a suitable Itoothed extension which is not shown in the drawings. For example, the push rod of FIG. 6 may be formed with teeth to constitute an extension of the rack 28.

FIGS. 8 to l() illustrate a modified mining apparatus which operates without a slide rail 24. This rail is replaced by a modified coupling device 41 which constitutes the lower pant of the gear case 31 and which guides the racks 27, 28 during the advance of the prop unit AA with respect to the unit BB, or vice versa. The modified apparatus is of more compact design and, furthermore, the racks 27, 28 are always at least partially protected by the greatly enlarged coupling device 41. The length of this coupling device equals at least one-half the length of a rack but preferably approximates the length of the rack 27 or 28 and, of course, the reducing `gearing 31 occupies only a fraction of its overall length. As is shown in FIG. l0, the coupling device 41 assumes the form of a double clevis, i.e. the form of a letter H in horizontal position. The web and the anges of this coupling device detine two elongated compartments 41a, 4111 which open laterally toward the prop units AA, BB, respectively, and which receive the main body portions and the teeth 27a, 28a of the racks 27, 28, respectively. The flanges of the coupling device 41 are formed with projections 42a, 42b which engage with the shoulders 27b, 28h, of the racks 27, 28, respectively, so that the racks are maintained in a position of parallelism with each other but are free to slide in the coupling device by traveling along the projections 42a, 42h. The ribs 27e, 28C of the racks 2'7, 28 project laterally outwardly from the respective compartments 41a, 41b and are releasably secured to spacer elements 44 by readily removable bolts 43. The spacer elements 44 are slidable along the aligned ilanges of upright guide members 21 one of which is mounted von each skid plate in the same manner as described in connection with FIGS. l to 7.

As is shown in FIG. 10, the compartments 41a, 41b fully receive and are nearly completely filled by the main body portions of the racks 27, 28 so that these racks, and particularly their teeth 27a, 28a, are normally protected against foreign matter or against other damage and become exposed only when the units AA, BB are shifted with respect to each other. In addition, the coupling 'device 41 insures a much better guidance of the racks 'during an advance of the modied mining apparatus.

The operation of the modified mining apparatus is analogous Ito the operation fof the apparatus shown in FIGS. 4 to 7. In FIG. 9, the front prop l5 off the unit BB is aligned with the rear prop 2 of the unit AA. When the unit BB is thereupon shifted by rotating the noncircular shaft 32 and the pinion in anticloclcwise direction, the rear prop 16 advances to the position of FIG. 9 in which it is aligned with the forward prop 1 `of the unit AA. Thus the positions of units AA, BB shown in FIGS. 8 and 9 correspond to the positions of units A, B in FIGS. 6 and 7. The length of steps which the units AA, BB can perform may be increased by increasing the :length of the racks 27, 28, i.e. these racks may extend ivell beyond the forward and rear ends of the respective prop units, if desired. The shaft 32 is again ydriven by a pneumatic or electric motor, not shown in FIGS. 8 to l0. It is further possible yto replace the I-bars 21 by other types of vertical guide members and to change the coniguration and the length of the couplingl device 4l.

It will be understood that each of the elements decribed above, or two or more together, may also nd a useful application in other types of mining apparatus diiiering from the types described above.

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can, by `applying current knowledge, readily adapt it for various yapplications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic and specic aspects or this invention and, therefore, such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the following claims.

What is claimed as new a-nd desired to be secured by Letters Patent is:

l. A mining apparatus comprising, in combination, a rst and a second prop unit, said units arranged side by side and each having roof engaging means for releasably engaging the roof of an excavation so as to hold the respective unit against movement with respect to the roof; and advancing means for stepwise moving said prop units with respect to each other in the same direction, said advancing means comprising a pair of parallel toothed racks, one for each of said units and each adapted to be secured to the respective unit so that displacements of said racks will cause displacements .ont the units, coupling means slidably connecting said racks to each other so that the rack of the unit which is disengaged from the roof may move with respect -to the rack. of the roofengaging unit, and shifting means for moving the racks with respect to each other and including a floating pinion meshing with said racks and drive means for rotating the pinion in clockwise .and anticlockwise directions to respectively move one of the racks with respect to the other rack and vice versa.

2. A mining 'apparatus as set lforth in claim 1, in which said drive means for rotating said pinion in clockwise and anticlockwise directions is a pneumatic motor.

3. A mining apparatus `as set forth in claim l, including releasable means for separably connecting said racks to the respective prop units.

4. A mining apparatus comprising, in combination, a first and a second prop unit, said units arranged side by side and each having roof engaging means for releasably engaging the roof of an excavation so as to hold the respective unit against movement with respect to lthe roof; and advancing means for stepwise moving said prop units with respect to each other in the same direction, said advancing means comprising `a pair of parallel toothed racks, one for each of ysaid units and each adapted to be secured to the respective unit so that displacements of said racks Will cause displacements of the units, coupling means slidably connecting said racks to each other 10 so that the rack of the unit which is ydisengaged from `the roof may move with respect to the rack of the rootengaging unit, and shifting means for moving the rack-s vwith respect to each other and including a oating pinion meshing with said racks and drive means for rotating the pinion in clockwise and anticlockwise directions to respectively move one of the racks with respect to the other rack and vice versa, said rotating means comprising a gear case slidably mounted on said racks and rotatably receiving said pinion, shaft means drivingly connected with said pinion, and motor means removably connected with said shaft means.

5. A mining apparatus comprising, in combination, a rst and a second prop unit, said units arranged side by side and each having roof engaging means for releasably engaging the roof of an excavation s0 as tophold the respective un-it against movement with respect to the roof; advancing means for stepwise moving sai-d prop units with respect to each other in the same direction, said advancing means comprising a pair of parallel toothed racks, one for each of said units and each adapted to be secured to the respective unit so that displacements of said racks will cause displacements of the units, coupling means slidably connecting said racks to each other so that the rack of the unit which is disengaged from the rood? may move with respect yto the rack of the roofengaging unit, `and shifting means for moving the racks with respect to eachother and including a floating pinion meshing with said racks and drive means Ifor rotating the pin-ion in clockwise and anticlockwise directions to respectively move one or" the racks with respect to the other rack and vice versa; and push rod means separably connected with and extending forwardly beyond one of `said racks.

6. A mining 4apparatus comprising, in combination, a first and a second prop unit, said units arranged side by side and each having roof engaging means for releasably engaging the roof of an excavation so as to hold the respective unit against movement with respect to the roof; and advancing means for stepwise moving said prop units with respect to each other in the same direction, said advancing means comprising a pair of elongated parallel toothed racks, one for each of said units and each adapted to be secured to the respective unit so that displacements or said racks will cause displacements of the units, coupling means slidably connecting said racks to each other so that the rack or the unit which is disengaged from the roof may move along said coupling means with respect to the rack of the roof-engaging unit, the length of said coupling means at least equal to the length of one of said racks, and shifting means for moving the racks with respect to each other and including a iloating pinion meshing with said racks and drive means for rotating the pinion in clockwise and anticlockwise direction to respectively move one of the racks with respect to the other rack and vice versa.

7. A mining apparatus comprising, in combination, a irst and la second prop unit, said units arranged side by side and each having roof engaging means for releasably engaging the roof of -an excavation so as to hold the respective unit against movement with respect to the roof; and advancing means `for stepwise moving said prop units with respect to each other in the same direction, said advancing means comprising a pair of parallel toothed racks, one for each of said units and each adapted to be secured to the respective unit so that displacements of said racks Vwill cause displacements of the units, an elongated double clevis -for slidably coupling said racks to each other so that the rack of the unit which is disengaged from the roof may move with respect to said ydouble clevis and with respect to the rack of the roof-engaging unit and that the double clevis may move with respect to the rack of the roof-engaging unit, and shifting means for moving the racks with respect to each other and including a oating pinion meshing with said racks and drive means for rotating the pinion in .clockwise and anticlockwise directions to respectively move -one of the racksiwith respect to the other rack and vice versa.

8. A mining apparatus comprising, in combination, a iirst and a second prop unit, said units arranged side by side and each having roof engaging means for releasably engaging the roof of an excavation so as to hold the respective unit against movement with respect to the roof; advancing means for stepwise moving said prop units with respect to each other in the same direction, said advancing means comprising a pair of parallel toothed racks, releasable means for separably connecting each of said racks to one of said prop units, coupling means slidably connecting said racks to each other so that the rack of the unit which is disengaged from the roof may move with respect to the rack of the roofengaging unit, and shifting means for moving the racks with respect to each other and including a tloating pinion meshing with said racks `and drive means for rotating the pinion in clockwise and -anticlockwise directions to respectively move one of the racks with respect to the other rack and vice versa; and means for releasably connecting said pinion with one of said units whereby said one unit, upon disengagement yfrom the roof and upon disconnection from its rack may be moved with respect to the other unit in response to rotation of said pinion.

9. A mining apparatus comprising, in combination, a first and a second prop unit, said units arranged side by side and each comprising a front prop, a rear prop, a cap section connected to each of said props and connecting means articulately linking the cap section of the front prop with the cap section of the rear prop, said props adapted to move said cap sections into and out of engagement with the roof of an excavation so as to alternately hold the respective unit against movement with respect to the roof and to permit movement of the unit; advancing means for stepwise moving said prop units with respect to each other in the same direction, said advancing means comprising a pair of parallel toothed racks, one for each of said units and each adapted to be secured to the respective unit so that displacements of said racks will cause displacements of the units, coupling means slidably connecting said racks to each other so that that the rack of the unit which is disengaged from the roor" may move with respect to the rack of the roofengaging unit, and shifting means for moving the racks with respect to each other and including a oating pinion meshing with said racks and'drive means for rotating the pinion in clockwise and anticlockwise directions to respectively move one of the racks with respect to the other rack and vice versa.

10. A mining apparatus comprising, -in combination, a tirst and a second prop unit, said units arranged side by side and each having roof engaging means for releasably engaging the roof of an excavation so as to hold the respective unit against movement with respect to the roof; and advancing means for stepwise moving said prop units with respect to each other in the same direction, said advancing means comprising a pair of elongated parallel toothed racks, one for each of said units, releasable means coupling the racks to the respective unit, coupling means slidably connecting said racks to each other so that the rack of the unit which is disengaged from the roof may move with respect to the rack of the roof-engaging unit, an elongated rail slidably connected with said racks `for guiding the same during movement of the racks with respect to each other, said rail having stop means at each of its ends engageable with said racks whereby the rack which moves with respect to the other rack may engage one stop means and entrains the rail in the same direction to move the other stop means into engagement with the other rack, and shifting means for moving the racks with respect to each other and including a oating pinion meshing with said racks and drive means for rotating the pinion in clockwise and anticlockwise directions to respectively move one of the racks with respect to the other rack and vice versa.

References Cited in the tile of this patent UNITED STATES PATENTS 2,910,281 Wilkenloh et a1 Oct. 27, 1959 2,965,412 Henderson et al. Dec. 20, 1960 FOREIGN PATENTS 920,316 Germany Nov. 18, 1954 786,331 Great Britain Nov. 13, 1957 1,190,532 France Apr. 6, 1959 

1. A MINING APPARATUS COMPRISING, IN COMBINATION, A FIRST AND A SECOND PROP UNIT, SAID UNITS ARRANGED SIDE BY SIDE AND EACH HAVING ROOF ENGAGING MEANS FOR RELEASABLY ENGAGING THE ROOF OF AN EXCAVATION SO AS TO HOLD THE RESPECTIVE UNIT AGAINST MOVEMENT WITH RESPECT TO THE ROOF; AND ADVANCING MEANS FOR STEPWISE MOVING SAID PROP UNITS WITH RESPECT TO EACH OTHER IN THE SAME DIRECTION, SAID ADVANCING MEANS COMPRISING A PAIR OF PARALLEL TOOTHED RACKS, ONE FOR EACH OF SAID UNITS AND EACH ADAPTED TO BE SECURED TO THE RESPECTIVE UNIT SO THAT DISPLACEMENTS OF SAID RACKS WILL CAUSE DISPLACEMENTS OF THE UNITS, COUPLING MEANS SLIDABLY CONNECTING SAID RACKS TO EACH OTHER SO THAT THE RACK OF THE UNIT WHICH IS DISENGAGED FROM ONE ROOF MAY MOVE WITH RESPECT TO THE RACK OF THE ROOFENGAGING UNIT, AND SHIFTING MEANS FOR MOVING THE RACKS WITH RESPECT TO EACH OTHER AND INCLUDING A FLOATING PINION MESHING WITH SAID RACKS AND DRIVE MEANS FOR ROTATING THE PINION IN CLOCKWISE AND ANTICLOCKWISE DIRECTIONS TO RESPECTIVELY MOVE ONE OF THE RACKS WITH RESPECT TO THE OTHER RACK AND VISE VERSA. 